The present invention is directed to protection for a battery pack, and especially to improving operation of a protection device associated with a battery pack in a very low power state.
A battery pack may be in a very low power state for one of several reasons. For example, a battery pack may be in a very low power state because it is nearly fully spent or drained. A battery pack may be in a very low power state because it is a new battery pack that has never been charged up.
Yet another reason that a battery pack may be in a very low power state is because its protection mechanism or system (i.e., electronics circuitry associated with and usually integrally housed with a battery pack) has been ordered into such a low power state. Battery packs typically have a number of different power states, such as a NORMAL state which is extant during normal operations of a unit powered by a battery pack. Another power state often used with a battery pack is a SLEEP state. A SLEEP state is usually employed after no operation of the device powered by the battery pack is noted for a predetermined time.
An example of such a situation is there not having been any key strokes entered to a laptop computer for a given time interval so the laptop computer orders its battery pack to a SLEEP state or mode. In such a SLEEP state the laptop battery pack powers fewer functions of the laptop and thereby conserves battery power for later availability when the laptop is being used. This is a way to extend useful battery life for a battery-powered device. It is typical that safeguards are still in place to protect the battery pack when a laptop orders the battery pack into a SLEEP state. Representative safeguards include, by way of example and not by way of limitation, protection against over-voltage, under-voltage, overload, over-current and short-circuit.
Another power state into which a battery pack may be placed is known as a SHIP state (sometimes referred to as a SHUTDOWN state). A SHIP power state is a sort of extended sleep mode that is generally employed for extending shelf life of a battery pack or for conserving battery power during other lengthy dormant periods such as when the battery pack is in shipment. When a battery pack is in a SHIP state or mode it is in a very low power mode (or, ultra-low power mode) during which power is conserved to a great degree by denying of power to various functions, including by way of example and not by way of limitation, the “gas gauge” function for relating amount of power used and safety FET (field effect transistor) control. Safety FETs are provided to isolate the battery pack from voltage or current that exceeds the safe operating parameters of the battery chemistry to the point of rendering the cells unusable and un-repairable.
There is a need for an apparatus for improving protection of a battery pack when the battery pack is in a very low power state.